JPH0392747A - Acoustic density meter - Google Patents

Abstract

PURPOSE:To make the temperature, pressure and viscosity of fluid hard to give effects and to achieve convenient handling with a simple structure by obtaining the density of the fluid in a pipe based on the pressure gradient and the acceleration of the fluid in the pipe which is measured with a detector. CONSTITUTION:The sine wave signal outputted from a sine-wave oscillator 10 is applied to a diaphragm 5 of a speaker through an amplifier 8. Thus, the fluid in a measuring pipe 2 is vibrated. The output sine wave from the oscillator 10 is inputted into a multiplier 12. The phase of the output sine wave is made to advance by 90 deg. in a phase device 11. The obtained cosine wave is inputted into a multiplier 12'. The pressure in the measuring pipe 2 is guided into a differential converter 7 through waveguides 3 and 3'. The differential pressure DELTAp between the outputs is multiplied by sinomegat and cosomegat in the multipliers 12 and 12', respectively. The (x) and (y) components Ex and Ey of the pressure gradient are inputted into a substractor 14 through LPFs 13 and 13'. The density is obtained by substraction and inputted into an indicating instrument 15.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for measuring the density of gases and liquids, and particularly to a device for measuring the density of a fluid from pressure gradient fluctuations that occur when vibrational acceleration is applied to the fluid to be measured. Involved.

Conventional methods for measuring fluid density include: Laboratory methods include methods that measure the weight of a fixed volume of the fluid to be measured, and methods that utilize the buoyancy of fluids such as floats and gas balances. A method suitable for measuring density from time to time in process lines, etc. is a method that utilizes the fact that the resonant frequency of a tube filled with the fluid to be measured or a vibrating element immersed in the fluid changes depending on the fluid density. A method that utilizes the fact that when one of two impellers is rotated, the torque generated in the other changes depending on the density of the fluid around the impeller, a method that measures the liquid column pressure at a constant height, and gamma rays. This method takes advantage of the fact that the rate of absorption changes depending on the density of the material.

The present invention is based on the relationship between the density of a fluid, the acceleration of the fluid, and the pressure gradient in the fluid, and the equation of motion. be.

An object of the present invention is to realize a density meter that is not easily affected by the temperature, pressure, and viscosity of the fluid to be measured, has a simple structure, and is easy to handle, based on a new operating principle different from conventional methods.

Hereinafter, the configuration of the present invention will be explained using FIG. 1 corresponding to an embodiment. In FIG. 1, 1 is a pipe through which a fluid to be measured having a density ρ flows, and 2 is a measurement pipe connected to 1 and filled with the fluid to be measured.

3 and 3° are pressure guide pipes connected to the sinusoidal tube 2 at a distance L, and guide pressure to the differential pressure converter 7.

4 is a back pipe connected to the end of the measuring pipe 2 and connected to the pipe 1; Reference numeral 5 denotes a vibrator fixed to the measuring tube 2, which is driven by an amplifier 8 to vibrate the fluid inside the tube. The back tube 4 is
Since it is provided to make the pressures before and after the vibrating membrane of the speaker 5 approximately equal, it is not necessarily necessary to provide it when the pressure inside the tube 1 is approximately equal to atmospheric pressure. Alternatively, 6 may be connected to 1 on the upstream side of the measurement tube 2. Differential pressure detector 7
is used to detect the pressure gradient in the measuring tube 2, as will be explained later. Reference numeral 6 denotes a speed pickup for detecting the vibration speed of the diaphragm of the speaker 5, 9 a subtracter, and lO a sine wave oscillator that outputs a sine wave sinωt of a constant frequency.

5, 6, 8 and 9 constitute a speed servo system, and the diaphragm of the speaker 5 receives the output signal si of the sine wave oscillator 10.
It vibrates at a constant amplitude speed with the same waveform as nωt. When the frequency of the oscillator 10 is set to a low frequency such that the wavelength of the sound caused by the vibration of the fluid to be measured is sufficiently longer than the entire length of the measuring tube 2, the fluid in the measuring tube 2 vibrates as a unit in the tube axis direction. The vibration velocity U is also a signal U with a constant amplitude and the same waveform as sinωt. It becomes sinωt. 11 is a phase shifter, IO
The phase of the output signal of the differential pressure converter 7 is advanced by 90'' to output COSωt. 12 and 12' are multipliers, and 13 and 13 are low-pass filters. Output signal sinω of oscillator 10
The output of l2 is smoothed by a low-pass filter 13 to produce a signal E.t. bawl. Similarly, the output signal of the differential pressure converter 7 and the output signal COSωt of the phase shifter 1 are as follows:
The signal Ey is multiplied by 12° and smoothed by 13°. In short, 12, +2'. 13 and 13' constitute a synchronous rectifier circuit, and output a signal E.13, which represents the magnitude of the component in phase with sinωt of the output signal of the differential pressure converter 7. The output of the signal E, which represents the magnitude of the component in phase with COSωt, plays the role of removing noise components. 14 is a subtracter, and 15 is an indicator.

θ1j When the fluid in the fixed tube 2 is moving in the tube axis direction at a speed U, the following equation of motion holds true.

p − a u/a t=-a p/a x (
1) Here, L represents time, p represents pressure, and X represents distance in the tube axis direction. 14”luo S as mentioned above]
Since nωt, the fluid acceleration a u /at is equal to ωuocosωt. On the other hand, since the frequency of the vibration velocity is such a low frequency that the wavelength is sufficiently longer than the entire length of the measuring tube 2, the axial pressure gradient within the measuring tube 2 is equal everywhere. Therefore, if the differential pressure measured at a distance within the measuring tube 2 is △p, then a p / a x - △p/t (
2) holds, and the differential pressure △p is the pressure gradient δp / a
Proportional to x. From equations (1) and (2), Δp−−ρtωuocosωt (3),
The differential pressure Δp becomes a cosine wave signal. Therefore, the signal Ey becomes a signal proportional to the amplitude of Δp, and since the magnitudes of t and ωUO are constant, the signal Ey becomes a signal representing the magnitude of the fluid density ρ. On the other hand, signal E9 is zero. In FIG. 1, instead of inputting Ey directly to the indicating instrument, the signal E. The reason why it is input to the indicator after it is removed is to enable accurate measurement of the density of highly viscous fluids.

Next, we will discuss the case where the viscosity of the fluid is high and its influence appears. Now, assuming that the measurement tube 2 is a tube with a circular cross section, the differential pressure △p when there is an influence of viscosity is expressed as △p=-pLω(1+y)LIoCOS(dtptωy) from the equation of motion.
uosinωt (4) ftanshiγ= (2 μ/ρω) l / 2 /
aμ is the viscosity coefficient, and a is the inner radius of the tube 2. That is, a component proportional to the vibration speed (sin (JJt component)) appears in Δp, and a component proportional to acceleration (cosωt component) increases compared to the case without viscosity.As can be seen from equation (4), , signal E
y is the size of (1+γ)(g when there is no viscosity,
Signal E. is a signal that is γ times Ey when there is no viscosity. Therefore, by the subtractor 14, E. By subtracting , the correct density can be measured even for fluids with high viscosity. Even if the measurement tube 2 does not have a circular cross section, the same relational expression as equation (4) holds true (the magnitude of γ is different), so density measurement can be performed with the same configuration. Note that as can be seen from equation (4), when the radius a of the measuring tube 2 is increased and the angular frequency ω of the sine wave oscillator 10 is increased, the influence of viscosity becomes smaller. If appropriate a and ω are selected, the influence of viscosity can be almost ignored, except in the case of fluids with particularly high viscosity. In this case, the signal E, is transmitted to the indicating instrument 1.
The density meter can be configured by direct manual input to 5.

In the case of the embodiment shown in FIG. 1, since the shape of the measuring tube 2 is simple, when the density of the fluid flowing through the main tube l changes6, the fluid in the measuring tube is replaced in a relatively short period of time. , has the same density as the fluid in the mains. However, the time required is
It changes depending on the speed of the flow inside the main pipe 1, etc. The embodiment shown in FIG. 2 solves this drawback. In Fig. 2, 16 is a zumbling bomb that pumps a certain volume of fluid.
It is inhaled from the main pipe 1 through the measuring pipe 2 and discharged through the back pipe 4 to l. Thereby, when the fluid density in the main pipe changes, the fluid density in the measuring pipe becomes equal to the density in the main pipe within a certain short period of time. Here, as a pump,
Use a type that sucks in and discharges fluid in a pulsating manner. Then, the velocity of the fluid in the measurement tube 2 in the tube axis direction also pulsates, and the fluid is subjected to vibrational acceleration. For example, when a Roots blower is rotated at a constant speed, the flow velocity in the measuring tube 2 pulsates, and the pulsation waveform is determined by the shape and rotational speed of the Roots blower. That is, in this embodiment, sampling of the fluid to be measured and application of acceleration to the fluid to be measured are performed by one sampling pump. 17 is a power source that drives the →nombling bomb. The wavelength of the sound in the measured fluid due to pulsation is τJ! It is driven under the condition that it is sufficiently long compared to the entire length of the II fixed tube 2. A pressure transducer 18 detects the pressure inside the measuring tube 2 guided by the pressure guiding tube 3. Fluctuations in the axial pressure gradient occur in the measurement tube 2 due to the pulsation of the fluid, but since the frequency of the pulsation is low, the pressure gradient is equal throughout the measurement tube 2. On the other hand, measurement tube 2
At the end of the pipe where it connects with main pipe 1, the pressure is constant. Measuring the pressure fluctuation at a point t° from the tube end with a pressure transducer is therefore equivalent to measuring the pressure gradient fluctuation in the measuring tube 2. Note that the pressure detector 18 may be attached to the back tube 4 instead of the measurement tube 2. However, in this case, the polarity of the signal is reversed. Reference numeral 19 denotes a synchronization signal generator, which outputs a sine wave of constant amplitude and in phase with the fundamental wave of the acceleration waveform of the fluid. 12 is a multiplier, l3 is a low-pass filter, and 15 is an indicator.

Since the flow velocity in the measuring tube 2 is determined by the shape and operating speed of the sampling pump 16, the acceleration waveform of the fluid is also determined.
The magnitude of the pulsation is constant.

The equation of motion (1) also holds true for the fluid in the measuring tube 2. Therefore, the output of the pressure transducer 18 has a waveform similar to the acceleration waveform, and the magnitude of the fluctuation is proportional to the density of the fluid to be measured. By multiplying the output of the synchronization signal generator 19 and the output of the pressure transducer 18 and smoothing the result, a signal E which is proportional to the magnitude of the fundamental wave component of the pressure gradient fluctuation is generated. is obtained. Since the magnitude of the fundamental wave of pressure gradient fluctuation is proportional to the magnitude of the entire pressure gradient fluctuation, signal E. is proportional to the density of the fluid being measured. Note that the reason why the density was determined from the fundamental wave component of the pressure gradient using synchronous detection is to eliminate noise caused by the flow in the main pipe 1 and the like. When the signal-to-noise ratio is relatively large, it is not always necessary to perform synchronous detection; it is also possible to obtain a signal proportional to the density by passing the pressure transducer output through a bandpass filter and rectifying it. can. In addition, another synchronous signal generator is used to generate a ±1 binary signal whose positive and negative sides are reversed at an appropriate phase in synchronization with the rotation of the sampling bomb, and perform synchronous detection or generate an acceleration waveform. Correlation detection may also be performed.

As is clear from the principles described above, if a bomb such as a Roots blower is connected to the main pipe l through which the fluid flows and there is pulsation in the flow, it is not necessary to provide the measurement pipes 2 and 4. Instead, the density can be determined by directly measuring the pressure gradient in the main pipe. Furthermore, when the viscosity of the fluid is high, the influence of viscosity can be removed by using a signal component proportional to the pulsation velocity of the fluid, that is, a signal orthogonal to the acceleration component, as in the embodiment shown in FIG. .

As described above, the present invention determines the density based on the equation of motion established between the density of the fluid, the acceleration, and the pressure gradient, and by knowing the oscillatory acceleration and the pressure gradient fluctuations that occur accordingly. To apply acceleration to the fluid, a subaker was used in the embodiment shown in FIG. 1, and a Sambunong pump was used in the embodiment shown in FIG. In this way, various methods can be considered for means for applying acceleration to fluid, means for detecting pressure gradients, electronic circuits for signal processing, etc., and these specific methods will explain the essence of the present invention. is not influenced by Moreover, it goes without saying that its use is not limited to measuring the density of fluid flowing inside a pipe. The operating principle of the present invention is based on the equation of motion, one of the most fundamental physical laws. Therefore, the operating principle of the present invention is valid under any temperature, pressure, etc. conditions. Therefore, it is possible to measure density without being affected by these conditions. Fluid viscosity is related to the equation of motion, but since the relationship is clearly known, its influence can be easily removed as described above.

In addition, the density meter of the present invention has a simple structure, and
It has the advantage of being easily realized and easy to handle.

Another feature of the present invention is that it is not affected even if dust in the fluid adheres to the movable parts.

[Brief explanation of drawings]

FIG. 1 shows one embodiment of the invention, and FIG. 2 shows another embodiment of the invention. ]... Fluid flowing pipe, 2... Measuring tube, 3, 1 2 3°... Impulse tube, 4... Back pipe, 5... Speaker, 6... Speed Big up, 7...Differential pressure converter, 8...Amplifier, 9...Subtractor, lO.
... Sine wave oscillator, 11 ... Phase shifter, 12, 12゜ ... Multiplier, 13, 13゛ ... Low pass filter, 14 - Subtractor, 15 ... Indicator, 16 -・・・
Sambunong pump, l7...power supply, 18...
Pressure transducer, 19... synchronization signal generator.

Claims (1)

[Claims] 1. Consists of a tube filled with fluid, means for applying vibrational acceleration to the fluid in the tube, and a detector that measures fluctuations in the pressure gradient in the tube, and the pressure gradient measured by the detector. A density meter characterized in that the density of the fluid in the pipe is determined from the acceleration and the acceleration.